The Bohai Strait is a crucial pathway for water exchange between the Bohai Sea and the Yellow Sea, and exhibits a robust spatiotemporal pattern of hydrodynamic conditions. 16S rRNA amplicon sequencing was applied to study the spatiotemporal patterns of bacterial community composition and diversity in the Bohai Strait. Physical and chemical parameters were measured in order to explain what might control the observed patterns in community composition and diversity. In response to environmental changes between seasons, especially the dramatic changes of temperature and nutrient (NO2-N and PO4-P) levels, Synechococcus and unclassified genera in Family I predominated in summer while some oligotrophic taxa (e.g., Pelagibacter, OM43 clade) are more abundant in winter. The spatial heterogeneity and overall patchiness of bacterial assemblages in the Bohai Strait could not be well explained by the measured factors. However, the taxa with the most spatially variable presence and absence, e.g. Vibrionaceae, SAR11 and Sva0996 marine group, possess differentiated niches for utilization of organic matter (OM) and display a close relationship with the distribution of OM sources in this area, which may indicate the significance of OM sources to bacterial community structure. Our results suggest that local factors rather than regional factors, such as dispersal limited by hydrodynamics, structure the bacterial communities in the Bohai Strait.